High power vacuum fuse



June 22, 1965 J. E. JENNINGS HIGH POWER VACUUM FUSE Original Filed June 13, 1961 INVENTOR.

J0 ZMMETTJ /VA///V65 $15 ATTORNEY United States Patent 3,190,986 HIGH POWER VACUUM FUSE Jo Emmett Jennings, La Selva Beach, Calif., assignor, by mesne assignments, to Jennings Radio Manufacturing Corporation, San Jose, Calif., a corporation of Delaware Continuation of application Ser. No. 116,813, June 13,

1961. This application Nov. 23, 1962, Ser. No. 240,212 13 laims. (Cl. 200-420) This application is a continuation of copending application Serial Number 116,813 filed June 13, 1961, now abandoned.

My invention relates to fuses enclosed within a vacuumized envelope; and particularly to such a fuse suitable for use as a circuit breaker in equipment where the occasional fault interruption can be accommodated, and the circuitry reactivated Without the much higher expense of a conventional circuit breaker.

An object of the invention is the provision of a vacuum fuse in which the vacuumized envelope can be opened and reloaded with a new fuse link, then reconditioned for continued use.

Another object of the invention is the provision of an electrically discontinuous shield structure surrounding the fuse link to intercept the particles driven toward the interior wall when the fuse blows without thereby providing a conductive path capable of short circuiting the fuse; and which when necessary may also be reconditioned and replaced in the envelope when the fuse is replaced.

Another object of the invention is the provision of a multiple-unit shield in which many or few separatedunits of the same size, but in number according to the length of the envelope, may be built up readily into a stable, strong, electrically discontinuous protective barrier between the heat and speeding particles of a blowing fuse and the enclosing envelope.

Other objects of my invention include a resilient support at each end of the fuse link which maintains a desired tension on the link to compensate for its expansion when heated; and provide an adjustability of such tension when the fuse is put in place in accordance with requirements inherent in the metal of the fuse link.

Other objects will appear in the following description of my invention, in which I do not limit myself to the showing made by said description and drawings, since I may use variant forms of the invention within the scope of the appended claims.

Referring to the drawings:

FIG. 1 is a vertical half-section of my vacuum fuse. A portion of the structure is omitted to reduce the length of the figure. The fuse link is of Wire type.

FIG. 2 is a horizontal section taken in the plane indicated by the line 2-2 of FIG. 1.

FIG. 3 is a fragmentary view in elevation. The direction from which the view is taken is indicated by the arrow 3 in FIG. 1.

FIG. 4 is a perspective view of one end of a flat fuse link including heat sinks.

My vacuum fuse comprises a generally cylindrical dielectric shell which with metallic ends forms an envelope in the longitudinal axis of which a fuse link is held under slight tension. The ends of the link are adjustably se cured in resilient mounting bracket means terminating on the outside of the envelope in terminal and mounting studs through which the fuse link is connected into a circuit. The inside of the shell is protected against the high heat and bombardment of metallic particles which follows blowing of the fuse, by a shield formed by a series of separate but overlapping peripherally continuous amass Patented June 22, 1965 ice metallic units supported in spaced stable assembly within the envelope and closely adjacent to the inside surface of the dielectric shell.

An end of the envelope may be removed and the assembled shield as well as the fuse link or its remnants taken from the shell for repair and/or replacement. The end plate is then hermetically rejoined to the shell, and the envelope processed to the required vacuum so that it may be continued in service. The cost of such renewal of the fuse link is but a fraction of the cost of replacing the entire vacuum fuse.

As a protective device my vacuum fuse is used in the same service as conventional domestic fuses, but it also must interrupt over-loads or withstand extremely high fault currents.

My present design is suitable for voltages of 12, kv. and up according to the characteristics of the fuse metal and the dimensions of the link. Fuse links which embody heat sinks may be used to delay blowing.

in terms of greater detail my high power vacuum fuse comprises a cylindrical glass shell 2, having flared end portions 3 in which a copper end ring 4 is hermetically sealed. At one end (bottom FIG. 1) the end ring is closed by an end plate 6 integral with the associated ring, but at the other (top) end, the ring 4 is closed by the end plate 7, integrally united to the ring by matching annular flanges 8 and 9 integral respectively with the plate 7 and ring 4. The flanges are connected around their periphery by brazing or heliarc union; and this joint is broken when the end plate is to be removed.

Assembled in place before the joining of the flanges 8 and 9 is the shield comprising a plurality of assembled but electrically discontinuous cylindrical units 11, each unit being formed by the union of an upper cylindrical section 12, having an outwardly extending radial flange 13, and a lower cylindrical section 14, having an outwardly extending flange 16 formed with an upwardly extending bead 17 for seating the abutting edge of the cylindrical section 12. The two sections are preferably brazed together at the head for greater security, especially in the larger embodiments of my invention. The outside diameter of the flanges 16 is slightly less than the inside diameter of the shell; and the outer diameter of the flanges 13 is still less than that of flanges 16.

Each of the flanges 13 and 16 is provided with four circumferentially spaced holes which permit the shield units to be assembled over ceramic spindles 18. Spacers 19 made of ceramic or other dielectric tubing, are threaded on the spindles between the flanges 13 and 16 of adjacent shield units 11; and longer spacers 21 at the lower end of the spindles support the shield assembly and fix its position in the envelope.

Coil springs 22 are interposed between the upper ends of the spindles and the end plate 7; and a spacer 23 encloses each spindle end and spring between the top flange 13 and the end plate so that the entire shield assembly is held securely lengthwise between the end plates and laterally by engagement of the central flanges 16- of each unit with the wall 2. Satisfactory shield units may be made of copper, nickel, molybdenum or stainless steel.

While my shielding means has been explained in its application to a vacuum fuse, it is obvious that it would be equally useful in any vacuumized envelope in which an are or electric discharge may occur, such for example between the contact points of a switch.

It will be noted that the assembled shield units as shown in FIG. 1 provide an overlapping of the larger cylindrical section 12 of one unit by the smaller cylindrical section 14 of the next higher unit, .and that the long narrow annular passage between the sections and the spacing between the units due to the interposition of spacers 19 insure an extensible electrically discontinuous shield on which metallic deposits cannot provide a path for high voltage flashove-r or shorting discharge.

t Mounted centrally in the envelope is the fuse link 27, which in FIG. 1 is shown as a copper wire. Other metals and alloys of different shapes, and including heat sinks 28 as suggested in FIG. 4, may be used. Each fuse link is provided at its ends with a fixed copper sleeve 29 threaded on the outside to adjustably engage a resilient mounting bracket or suspension means arranged on the inside end of the terminal studs.

The bottom stud 31 preferably of copper extends through the end plate 6 and at .its inner end is provided with a double loop 31 of flat rectangular cross section to form a resilient bracket. The thickened end 32 of the loop is provided with a threaded hole 33 in which the threaded sleeve 29 on the fuse link end may be secured by turning.

. At the upper end of the envelope, a copper terminal stud 36 is brazed in the end plate '7. A tubulation 37 is brazed into the stud as shown to provide a continuation of the passage 38, opening into the envelope and through which the envelope is exhausted after hermetic sealing is completed.

Brazed across the center of the inside face of the stud, but not closing the opening therein, is a copper tube 39, looped as shown to give it resilience as a mounting bracket, on the free end 41 of which a socket block 42 is brazed. The socket is threaded to receive the sleeve 29, and the several parts are so proportioned that the fuse link is subjected to a small amount of tension because of bias in the spring mounting means at each end.

In the final assembly of my vacuum fuse, and after the shield assembly has been completed, the fuse link is screwed into the socket block 42 and its lower end started in the loop end 32. The end plate 7 is then turned a few times to seat the flange 8 against the flange 9, at which time the lower end of the fuse link will have fully seated in its spring bracket. The edges of the flanges 8 and 9 are then fused or brazed together, and the envelope is (ready for evacuation and final processing.

. It will be obvious from the foregoing that upon blowing of the fuse link, the envelope may be opened at the flanges and the remnants of the fuse including the copper sleeves 29 removed. If inspection of the shield assembly shows damage, the injured unit is replaced. A new fuse link is then seated in the top bracket, and closing the envelope, seating the lower end of the fuse link, resealing and processing proceeds as during the first assembly.

Instead of a vacuumized envelope, my fuse structure may be used with an envelope filled with an inert gas such as nitrogen, or with a mixture of inert gases.

Iclaim:

=1. A fuse structure, comprising an envelope having a dielectric shell and metallic end plates hermetically attached to the open ends of the shell, a terminal stud on each end plate, a fuse link having its ends secured to the terminal studs and comprising a continuous conductor gauged to take a predetermined level of electric current between said terminal studs and adapted to melt rapidly to form a non-conductive discontinuity in said conductor when said predetermined current level is exceeded, a shield interposed between said fuse link and said dielectric shell and including a plurality of separate cylindrical units, each unit having a pair of flanges extending radially therefrom, and a plurality of dielectric spindles supported between said end plates and engaging each pair of flanges to fix the position of the shield in the envelope.

2. A fuse structure in accord with claim 1 in which one of the flanges of each unit engages the inner wall surface of the envelope to give lateral stability to the shield.

3. A fuse structure in accord with claim 1 in which spring means are interposed between the end of each spindle and the adjacent end plate.

4. A fuse structure in accord with claim 1 in which dielectric spacers are interposed between the flanges of adjacent shield units to electrically insulate said adjacent shield units from each other.

5. A fuse structure in accord with claim 1 in which each of the shield units comprises cylindrical portions of different diameters, each portion carrying one flange of said pair of flanges and one of the flanges being of a diameter to engage the inner wall of the envelope.

6. A fuse structure in accord with claim 1 in which one of the flanges of each unit engages the inner wall surface of the envelope and dielectric spacers are interposed between the flanges of adjacent shield units. 7. A fuse structure in accord with claim 1 having united flanges readily disjoinable and having one of said flanges joined to the shell and the other joined to one of the end plates whereby the flanges hermetically attach said end plate to the shell and may be disjoined to permit removal of the shield and thermally ruptured fuse link parts from the envelope.

8. A shield for the inside wall of an envelope, comprising a plurality of similar cylindrical units, each unit having cylindrical sections of differing diameters and having upper and lower radial flanges thereon, said radial flanges having a plurality of sets of vertically aligned holes spaced circumferentially therearound, a dielectric spindle extending through each of the corresponding sets of aligned holes and bearing at its ends against the end walls of the envelope, and a dielectric spacer between the upper flange of one unit and the lower flange of the adjacent unit.

9. A shield for the inside wall of an envelope in accord with claim 8 in which one of the radial flanges is of such diameter as to engage the inside surface of the envelope wall.

It A fuse, comprising a hermetically sealed envelope having oppositely disposed end plates, 2. terminal stud on each end plate and extending therethrough to the interior of said envelope, a conductive mounting bracket secured on the inner end of each terminal stud and resiliently biased in a direction away from each other, and a fuse link having an end secured in each bracket and held under tension by the resilient bias of said mounting brackets.

11. A fuse in accordance with claim it? in which one of the end plates is joined to the envelope by thin adjacent flanges integrally united about their periphery by a sever-able union.

12. A fuse, comprising a hermetically sealed envelope having oppositely disposed end plates, a terminal stud on each end plate extending therethrough to the interior of said envelope, a conductive mounting bracket secured on the inner end of each terminal stud, a fuse link having an end secured in each bracket, a shield including a plurality of separate cylindrical units spaced from and surrounding the fuse link to intercept the hot discharge of high velocity fuse particles when the fuse link ruptures, and dielectric means interposed between the shield and envelope for supporting said units in electrically discontinuous assembly.

13. A fuse, comprising, a hermetically sealed envelope having oppositely disposed end plates, a terminal stud on each end plate extending therethrough to the interior of said envelope, a conductive mounting bracket secured on the inner end of each terminal stud, a fuse link having an end secured in each bracket, a shield including a plurality of separate cylindrical units spaced from and surrounding the fuse link to intercept the hot discharge of high velocity fuse particles when the fuse link ruptures, and dielectric means interposed between the shield and envelope for supporting said units in electrically discontinuous assembly, said conductive mounting bracket including a resilient portion to maintain the fuse link under tension.

(References on following page) References Cited by the Examiner UNITED STATES PATENTS Davis 200-132 Bronson 200-132 Sorensen et a1 200-131 5 Steenbeck 313313 Ludwig 200-131 BERNARD A. GILHEANY, Primary Examiner. 

1. A FUSE STRUCTURE, COMPRISING AN ENVELOPE HAVING A DIELECTRIC SHELL AND METALLIC END PLATES HERMETICALLY ATTACHED TO THE OPEN ENDS OF THE SHELL, A TERMINAL STUD ON EACH END PLATES, A FUSE LINK HAVING A CONTINUOUS CONDUCTOR TERMINAL STUDS AND COMPRISING A CONTINUOUS CONDUCTOR GAUGE TO TAKE A PREDETERMINED LEVEL OF ELECTRIC CURRENT BETWEEN SAID TERMINATED STUDS AND ADAPTED TO MELT RAPIDLY TO FORM A NON-CONDUCTIVE DISCONTINUITY IN SAID CONDUCTOR WHEN SAID PREDETERMINED CURRENT LEVEL IS EXCEEDED, A SHIELD INTERPOSED BETWEEN SAID FUSE LINK AND SAID DIELECTRIC SHELL AND INCLUDING A PLURALITY OF SEPARATE CYLINDRICAL UNITS, EACH UNIT HAVING A PAIR OF FLANGES EXTENDING RADIALLY THEREFROM, AND A PLURALITY OF DIELECTRIC SPINDLES SUPPORTED BETWEEN SAID END PLATES AND ENGAGING EACH PAIR OF FLANGES TO FIX THE POSITION OF THE SHIELD IN THE ENVELOPE. 